You missed the point. I suggest you read the Spyro crack protection article that was posted above.
Basically, they allowed the game to continue to be played for a short while so as to give the impression to crackers that they had successfully cracked the game. But then later on, when people try to play the cracked game, they realized an hour later that they couldn't beat it due to various necessary components missing.
That, and there are other layers of stuff stopping it as well, like full-out crashes, multiple checks hard coded into the game at completely random spots, checksums that check their own sums, etc. It's actually quite thorough.
The hard part wasn't really detecting that the pirates had cracked the code, but to simply make it appear as though it had been cracked at a glance. And then making it not more difficult for pirates to crack, but more time consuming. They realized that cracking was inevitable, but they were more interested in making it slow, painful work, not interesting, curious work.